LAUSR

The post-exposure effect of fatiguing noise (half-octave band-limited noise centered at 32 kHz) on the evoked responses to test stimuli (rhythmic pip trains with a 45-kHz center frequency) at various levels (from threshold to 60 dB above threshold) was investigated in a beluga whale Delphinapterus leucas. For baseline (pre-exposure) responses, the magnitude-vs-level function featured a segment of steep magnitude dependence on level that was followed by a segment of little dependence (plateau). Post-exposure, the function shifted upward along the level scale. Due to the plateau in the magnitude-vs-level function, post-exposure suppression of responses depended on the stimulus level such that higher levels corresponded to less suppression. The experimental data may be modeled based on the compressive non-linearity of the cochlea. According to the model, post-exposure responses of the cochlea to high-level stimuli are minimally suppressed compared to the pre-exposure responses, despite a substantially increa...